Proof-of-Concept Backport Invokedynamic in Groovy

It is my first day of Google Summer of Code, and here is what I've done today ;-)

I have been reading hard and trying to understand Invokedynamic EDR since last week. It is quite difficult for me, who has little background of this kind of things. However, I have got some good sources for studying how invokedynamic work from John Rose's blog, Alex Tkachman's Method Handle code, Jeroen Frijters's blog, and Rémi Forax's blog.

Although, there is no something complex like Jeroen's sample, here is a working version of Hello World that uses my backport of invokedynamic APIs.

package groovy.dyn.subject.vm5;

import groovy.dyn.CallSite;
import groovy.dyn.Linkage;
import groovy.dyn.MethodHandle;
import groovy.dyn.MethodHandles;
import groovy.dyn.MethodType;
import groovy.dyn.StaticContext;
import groovy.dyn.internal.CallSiteImpl;
import groovy.dyn.internal.StaticContextImpl;

import java.io.PrintStream;
import java.lang.reflect.Method;

public class InvokeDynamicSubject {

private static CallSite[] callsites;
private static final int NUM_OF_CALLSITES = 1;

static {
initCallSites();
try {
Method method = InvokeDynamicSubject.class
.getDeclaredMethod("bootstrapInvokeDynamic",
CallSite.class, Object.class, Object[].class);
MethodHandle mh = MethodHandles.unreflect(method);
Linkage.registerBootstrapMethod(InvokeDynamicSubject.class, mh);
} catch (Throwable e) {
// do nothing now
}
}

private static void initCallSites() {
callsites = new CallSite[NUM_OF_CALLSITES];
callsites[0] = new CallSiteImpl(0,
new StaticContextImpl(
PrintStream.class,
"println",
MethodType.make(void.class, String.class)
)
);
}

private static Object bootstrapInvokeDynamic(CallSite cs,
Object receiver, Object[] args) throws Throwable {
Method method=null;
CallSiteImpl csi = (CallSiteImpl)cs; // down cast: language specific
switch(csi.index()) {
case 0: {
StaticContext sc = cs.getStaticContext();
Class<?> c = sc.getCallingClass();
method = c.getDeclaredMethod(
sc.getName(),
sc.getType().parameterType(1));
MethodHandle mh = MethodHandles.unreflect(method);
cs.setTarget(mh);
return mh.invoke(receiver, args);
}
}
return null;
}

public void test() throws Throwable {
// System.out.println("Hello World");
MethodHandle mh = callsites[0].getTarget();
if(mh == null) {
bootstrapInvokeDynamic(callsites[0], System.out, new Object[]{"Hello World"});
} else {
mh.invoke(System.out, "Hello World");
}
}
}